1. Field of the Invention
This invention relates to amorphous metal magnetic components, and more particularly, to a high efficiency electric motor having a generally polyhedrally shaped bulk amorphous metal magnetic component.
2. Description of the Prior Art
An electric motor typically contains magnetic components made from a plurality of stacked laminations of non-oriented electrical steel. In variable reluctance motors and eddy current motors, the stators are made from stacked laminations. Both the stator and the rotor are made from stacked laminations in squirrel cage motors, reluctance synchronous motors and switched reluctance motors. Each lamination is typically formed by stamping, punching or cutting the mechanically soft, non-oriented electrical steel into the desired shape. The formed laminations are then stacked and bound to form the rotor or stator.
Although amorphous metals offer superior magnetic performance when compared to non-oriented electrical steels, they have long been considered unsuitable for use in bulk magnetic components such as the rotors and stators of electric motors due to certain physical properties and the corresponding fabricating limitations. For example, amorphous metals are thinner and harder than non-oriented steel and consequently cause fabrication tools and dies to wear more rapidly. The resulting increase in the tooling and manufacturing costs makes fabricating bulk amorphous metal magnetic components using such techniques commercially impractical. The thinness of amorphous metals also translates into an increased number of laminations in the assembled components, further increasing the total cost of an amorphous metal rotor or stator magnet assembly.
Amorphous metal is typically supplied in a thin continuous ribbon having a uniform ribbon width. However, amorphous metal is a very hard material, making it very difficult to cut or form easily, and once annealed to achieve peak magnetic properties, becomes very brittle. This makes it difficult and expensive to use conventional approaches to construct a bulk amorphous metal magnetic component. The brittleness of amorphous metal may also cause concern for the durability of the bulk magnetic component in an application such as an electric motor.
Another problem with bulk amorphous metal magnetic components is that the magnetic permeability of amorphous metal material is reduced when it is subjected to physical stresses. This reduced permeability may be considerable depending upon the intensity of the stresses on the amorphous metal material. As a bulk amorphous metal magnetic component is subjected to stresses, the efficiency at which the core directs or focuses magnetic flux is reduced resulting in higher magnetic losses, increased heat production, and reduced power. This stress sensitivity, due to the magnetostrictive nature of the amorphous metal, may be caused by stresses resulting from magnetic and mechanical forces during the operation of the electric motor, mechanical stresses resulting from mechanical clamping or otherwise fixing the bulk amorphous metal magnetic components in place, or internal stresses caused by the thermal expansion and/or expansion due to magnetic saturation of the amorphous metal material.
For certain high speed motors the core losses of typical electrical steels are prohibitive. In such cases a designer may be forced to use a permalloy alloy as an alternative. However, the attendant reduction in saturation induction (e.g. 0.6-0.9 T or less for various permalloy alloys versus 1.8-2.0 T for ordinary electrical steels) necessitates an increase in the size of magnetic components comprised of permalloy or variants thereof. Furthermore, the desirable soft magnetic properties of the permalloys are adversely and irreversibly affected by plastic deformation which can occur at relatively low stress levels. Such stresses may occur either during manufacture or operation of the permalloy component.
The present invention provides a low-loss bulk amorphous metal magnetic component having the shape of a polyhedron and being comprised of a plurality of layers of amorphous metal strips for use in highly efficient electric motors. Also provided by the present invention is a method for making a bulk amorphous metal magnetic component. The magnetic component is operable at frequencies ranging from about 50 Hz to 20,000 Hz and exhibits improved performance characteristics when compared to silicon-steel magnetic components operated over the same frequency range. More specifically, a magnetic component constructed in accordance with the present invention and excited at an excitation frequency xe2x80x9cfxe2x80x9d to a peak induction level xe2x80x9cBmaxxe2x80x9d will have a core loss at room temperature less than xe2x80x9cLxe2x80x9d wherein L is given by the formula L=0.0074 f (Bmax)1.3+0.000282 f1.5 (Bmax)2.4, the core loss, the excitation frequency and the peak induction level being measured in watts per kilogram, hertz, and teslas, respectively. Preferably, the magnetic component will have (i) a core-loss of less than or approximately equal to 1 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 60 Hz and at a flux density of approximately 1.4 Tesla (T); (ii) a core-loss of less than or approximately equal to 20 watts-per-kilogram of amorphous metal material when operated at a frequency of approximately 1000 Hz and at a flux density of approximately 1.4 T, or (iii) a core-loss of less than or approximately equal to 70 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 20,000 Hz and at a flux density of approximately 0.30 T. The reduced core loss of the magnetic component of the invention advantageously improves the efficiency of an electric motor which comprises it.
In a first embodiment of the present invention, a bulk amorphous metal magnetic component comprises a plurality of substantially similarly shaped layers of amorphous metal strips laminated together to form a polyhedrally shaped part.
The present invention also provides a method of constructing a bulk amorphous metal magnetic component. In accordance with a first embodiment of the inventive method, amorphous metal strip material is cut to form a plurality of cut strips having a predetermined length. The cut strips are stacked to form a bar of stacked amorphous metal strip material and annealed to enhance the magnetic properties of the material and, optionally, to transform the initially glassy structure to a nanocrystalline structure. The annealed, stacked bar is impregnated with an epoxy resin and cured. The stacked bar is then cut at predetermined lengths to provide a plurality of polyhedrally shaped magnetic components having a predetermined three-dimensional geometry. The preferred amorphous metal material has a composition defined essentially by the formula Fe80B11Si9.
In accordance with a second embodiment of the method of the present invention, an amorphous metal strip material is wound about a mandrel to form a generally rectangular core having generally radiused corners. The generally rectangular core is then annealed to enhance the magnetic properties of the material and, optionally, to transform the initially glassy structure to a nanocrystalline structure. The core is then impregnated with epoxy resin and cured. The short sides of the rectangular core are then cut to form two magnetic components having a predetermined three-dimensional geometry that is the approximate size and shape of said short sides of said generally rectangular core. The radiused corners are removed from the long sides of said generally rectangular core and the long sides of said generally rectangular core are cut to form a plurality of polyhedrally shaped magnetic components having the predetermined three-dimensional geometry. The preferred amorphous metal material has a composition defined essentially by the formula Fe80B11Si9.
The present invention is also directed to a bulk amorphous metal component constructed in accordance with the above-described methods.
Construction of bulk amorphous metal magnetic components in accordance with the present invention is especially suited for amorphous metal stators or stator components in highly efficient, variable reluctance motors and eddy current motors. Similarly, bulk amorphous metal components may be used as both the rotor and the stator in squirrel cage motors, reluctance synchronous motors and switched reluctance motors. It will be understood by those skilled in the art that such motors may comprise one or more rotors and one or more stators. Accordingly, the terms xe2x80x9ca rotorxe2x80x9d and xe2x80x9ca statorxe2x80x9d as used herein with reference to motors mean a number of rotors and stators ranging from 1 to as many as three or more. It will also be recognized by those skilled in the art that the term xe2x80x9celectric motorxe2x80x9d, as used herein, refers generically to a variety of rotating electrical machines which additionally comprise electric generators as well as regenerative motors that may be operated optionally as electric generators. The magnetic component of the invention may be employed in constructing any of these devices. The advantages recognized by the present invention include simplified manufacturing and reduced manufacturing time, reduced stresses (i.e., magnetostrictive) encountered during construction of bulk amorphous metal components, and optimized performance of the finished amorphous metal magnetic component.